This invention relates to machine leveling devices.
Many types of machinery and other devices require precision alignment or leveling for optimum performance. Examples of such devices include motors, pumps, turbines, presses, and scientific instruments and the like. At present many of these devices are leveled by using a simple screw-jack consisting of a bolt that provides a means of raising or lowering the device, threaded directly into the device or into a mount. U.S. Pat. No. 3,351,309 to Harrison discloses such a simple screw-jack type of adjustable mounting.
The use of a bolt as a load bearing "leg" for the support of machinery can pose difficulties if the machine is to be placed on a surface that varies in elevation between different mounting locations. Because the end of the bolt (or the bolt head if the bolt is used in an inverted position) is relatively flat and is fixed in a position perpendicular to the machine, any tilt in the bearing surface or floor will result in the machine load being transferred to the floor through only a portion of the end or head of the bolt. This causes a high concentration of stress in a small area of the bolt and the ultimate load bearing surface (i.e. the floor) that can result in bolt failure or shear failure of the loading surface.
A further drawback of using a simple bolt as a load bearing leveling means is frictional build-up between the bolt end or head and the bearing surface. As bolts at different locations are adjusted, the machine or other device tends to rotate about the leveling bolt that is being adjusted. This rotation is resisted by the remaining leveling bolts due to the "biting" action of the bolts into the bearing surface. As a result of this resistance, stress accumulates at the interface between the bolts and the bearing surfaces until the frictional force is overcome at which time the device "snaps" free and rotates or translates. Because the resulting motion is unpredictable, the number of adjustments required to level the device during the leveling process increases.
An alternate means of leveling machines and the like is through the use of plates or shims of various thicknesses placed under the supports of the devices. U.S. Pat. No. 4,809,421 to Justice discloses a shim for insertion between the base of a machine and a support bearing plate to adjust the spacing therebetween. Shims provide the advantage of transferring loads across a greater area than through bolt threads as screw-jacks do.
Shims do, however, have drawbacks of their own. The use of shims requires an external means of raising and lowering the device during installation and adjustment of the shims. Often times the use of shims is a trial and error process that requires shims of multiple thicknesses and a repeated number of raising and lowering cycles.
Shims are also difficult to use if the machine is to be placed on a surface that varies in elevation between different mounting locations. Because the device being leveled may be installed on a sloping surface, the bottom of the device may be tilted with respect to the lower shim surface facing the floor. If the shim has an upper surface parallel to its lower surface, the angle between the bottom of the device and the floor may cause the load to be transferred through only a small portion of the shim's bearing surface. A remedy for this problem is the fabrication of shims of variable cross-sections. This remedy is, however, impractical and cost prohibitive. The use of multiple shims and extremely thin shims is another alternative. Using such shims can, however, cause other difficulties as documented in the Justice '421 patent.